Amidate-Ligated Complexes of Rhodium(I): A Showcase of Coordination Flexibility

Reaction of the amidate ligand salts Na[N(Dipp)C(O)R] (R = Ph (1a), tBu (1b); Dipp = 2,6-diisopropylphenyl) with [Rh(NBD)-Cl](2) (NBD = norbomadiene) proceeds to give the dirhodium(I) complexes [Rh-2{mu(2)-N,O-N(Dipp)C(O)R}(2)(NBD)(2)] (R = Ph (2a), tBu (2b)) with variable coordination behavior. For complex 2b, a monomer-dimer equilibrium with the mononuclear complex [Rh{kappa(2)-N,O-N(Dipp)-C(O)tBu}(NBD)] (3b) was established for the first time. Precursors 2a,b were treated with PPh3 and PCy3, giving the distorted-square-planar kappa(2)-N,O amidates [Rh-{kappa(2)-N,O-N(Dipp)C(O)R}(PPh3)(2)] (R = Ph (4a), tBu (4b)) or the kappa(1)-O complexes [Rh{kappa(1)-O-N(Dipp)C(O)R}(NBD)(PCy3)] (R = Ph (5a), tBu (5b)). Initial reactivity screening showed that complex 4b undergoes O-2 activation, providing Ph3P=O; via the transient peroxo complex 6b, which was characterized in the solution phase. The kappa(2)-N,O amidate coordination in 6b has been conclusively established by diagnostic C-13{H-1} NMR spectroscopy.